Bisphenols, and in particular bisphenol A (2,2 bis(p-hydroxyphenyl) propane), have become industrially significant reactants for a number of processes including the preparation of polycarbonates. Bisphenols are prepared on an industrial scale by one of two processes: an acid-catalyzed or HCl process and an ion exchange process, in which an acidic ion exchange resin such as sulfonic acid-substituted polystyrene is employed. In the HCl process, the bisphenol is prepared by condensation of two moles of phenol with one mole of a ketone or aldehyde, for example acetone, in the presence of HCl. Processes for the production and purification of bisphenols are well known, and are described inter alia in U.S. Pat. Nos. 4,107,218; 4,294,994; 5,210,329; 5,243,093; 5,245,088; 5,288,926; 5,368,827; 5,786,522; and 5,874,644.
During the course of producing, bisphenols by this process, the solubility of the product bisphenol is not always high enough for all of the bisphelnol produced to be dissolved. As a result, the bisphenol may crystallize out as a bisphenol-phenol adduct on the inner surface of the reactor. This layer reduces heat exchange efficiency within the reactor, and hence limits reactor temperature control. The result is a lower quality product, and/or reduced plant capacity. Thus, the reactor used in the production of bisphenols needs to be cleaned periodically to remove any build-up of the bisphenol-phenol adduct. In accordance with known methods, this cleaning is done by either filling the reactor with pure phenol or by charging extra water or acid into the reactor. These actions increase the solubility of bisphenol in the mixture and built-up bisphenol-phenol adduct dissolves. Unfortunately, product produced during such cleaning does not meet specifications. This means that the time spent for cleaning is effectively down time for the reactor. There is therefore a need for a method for cleaning reactors used in the production of bisphenols which allows the cleaning to occur without significant production loss, plant instability or quality loss.